1. Field of the Invention
The present invention relates to a storage apparatus, a control method, a control circuit, and a program for reading/writing data by causing a head to fly over a rotating recording medium, and particularly relates to a storage apparatus, a control method, and a control circuit for controlling the flying height between a head and a recording medium surface to a predetermined target flying height by varying a protrusion value by thermal expansion which accompanies electric power distribution to and heating of a heater provided in the head.
2. Description of the Related Arts
Conventionally, the flying height of a head with respect to the recording surface of a magnetic disk has to be reduced in order to realize a high recording density of a magnetic disk apparatus, and a flying height of 10 nm order has been realized recently. However, when the flying height of the head is reduced, collision with minute protrusions on the magnetic disk surface is readily caused, and variation in the clearances between heads is present in the range of mechanical common differences; therefore, there is a problem that the flying height cannot be set lower than the range of common differences when the medium contact is taken into consideration. Therefore, recently, like Patent Document 1, there is proposed a method in which variation in the protrusion value (TPR value) caused by a phenomenon in which the head flying surface protrudes toward the direction of the magnetic disk due to temperature increase in a write head (thermal protrusion: TPR) is measured in an examination process or the like and retained in a magnetic disk, and the data is used for managing the flying height for each head. Furthermore, there have also been proposed methods like Patent Documents 2 and 3 in which a heater is incorporated in a head, and the clearance between the head and the recording surface of a magnetic disk is controlled by utilizing the protrusion phenomenon caused by thermal expansion of the head flying surface accompanying electric power distribution to the heater. In Patent Document 2, a constant element temperature is maintained by varying the electric power applied to an electricity conduction film provided on the head relative to increase in the apparatus temperature or the element temperature due to recording/reproduction, thereby maintaining a constant clearance between the element and the recording medium. In Patent Document 3, a flying-height-increasing heating device which increases the distance between the recording reproduction element and the magnetic disk surface by causing a part of an air bearing surface of the head to expand and protrude by heating, and a flying-height-reducing heating device which reduces the distance between the recording/reproduction element and the magnetic disk surface by causing another part of the head air bearing surface to expand and protrude by heating are provided in the head, and the flying height is corrected such that reproduction can be performed without causing collision during apparatus activation or the like.
However, in such conventional methods of controlling the flying height between the head and the magnetic disk recording surface, basically, the protrusion value is adjusted such that reproduction can be performed without causing medium contact by utilizing that the flying height is varied due to expansion/protrusion of the head flying surface along with electric power distribution to and heating of the heater; and there has been a problem that highly precise flying height control of controlling the flying height upon recording and reproduction to a constant target flying height by taking variation in the flying heights which are different in heads into consideration cannot be performed. In addition, there is a slight delay until the flying height is stabilized after it is varied by protrusion caused by thermal expansion after electric power is distributed to the heater. Therefore, in conventional flying height control using heater electric power distribution upon recording, the write starting part is not in the state that thermal expansion of the head is not completely saturated, and the flying height of the head is close to the recording medium and has not reached a target flying height; therefore, there is a problem that writing performance of a recording element is low, and the error rate is deteriorated at the writing started part. In order to solve this problem, electric power distribution to the heater is started from a target track position, and then writing is performed after waiting for one rotation; thus, thermal expansion of the head can be completely saturated so as to stabilize the target flying height, and the problem that the error rate is deteriorated at the writing starting part can be solved. However, there are problems that access performance is deteriorated since rotation waiting is required for thermal expansion saturation caused by heater electric power distribution; and, furthermore, electric power consumption is increased, and deterioration of the head element is accelerated since electric power distribution and heating using the heater is performed more than necessary. These problems are similarly generated also in conventional flying height control using heater electric power distribution upon reproduction.